Method of testing evacuated well pressure gauges



Feb. 20, 1951 w. R. POSTLEWAITE 2,542;355 METHOD OF TESTING EVACUATED WELL PRESSURE GAUGES Original Filed Dec. 26, 1944 3 Sheets-Sheet l William R. Posflewaife ATTORNEYS Feb. 20, 1951 w. R. POSTLEWAITE 2,542,355

METHOD OF TESTING EVACUATED WELL PRESSURE GAUGES Original Filed Dec. 26, 1944 /9 FIGS 3 Sheets-Sheet 2 FIG.7

William R. Posflewaife ATTORNEYS Feb. 951 w. R. POSTLEVIAITE 2,542,355

METHOD OF TESTING EVACUATED WELL PRESSURE GAUGES Original Filed Dec. 26, 1944 s sheets-sheet s William R. Posrlewaire Patented Feb. 20, 1951 METHOD OF TESTING EVACUATED WELL PRESSURE GAUGES William R. Postlcwaite, Menlo Park, Califl, as-, signor to California Research Corporation, San Francisco, Calif., a corporation of Delaware Original application December 26, 1944, Serial N 0.

Divided and this application December 30, 1946, Serial No. 719,302

1 Claim.

This invention relates to pressure recorders such as are used for determining the relation between pressure and depth or fluid flow conditions in oil wells, and particularly refers to a method of testing the degree of evacuation of one in which the deformation of an elastic member due to pressure changes is translated into changes of resistance of a coil of wire, the latter value being transmitted to the surface through a multiconductor electric cable to a suitable indicator.

Heretofore, pressure gauges which have been adapted to be lowered through the small diameter (two-inch) tubing of a flowing well, have utilized mechanical movements with pistons and packing glands, Bourdon tubes, bellows, coil springs, geared multipliers and the like, to respond to pressure variations in the ambient fluid in the well and to actuate recording apparatus at the bottom of the well. Due to space limitations the pressure responsive means and also the recording means therefor are necessarily quite small and inherently involve errors of the order of 2 or 3%. So long as well depths were relatively shallow and pressures involved were of the order of 2,000 or 3,000 pounds per square inch, these limitations were not so serious. Present practice, however, involves wells upward of 12,000 feet in depth and pressures ranging up to 6,000 pounds persquare inch. In order to reduce errors to less than of the indicated pressures, it is necessary that every precaution be taken to avoid complicated and elaborate arrangements, particularly where mechanical features are involved.

This invention comprehends broadly the provision of an elongated housing adapted to be lowered into a small diameter well tubing and to contain a hollow member having a generally tubular configuration and made of an elastic material having relatively high strength, for example ductile tungsten, nickel-iron alloy steel, fused quartz, or the like, and with which is associated on either its inner or outer surface a bonded filament resistance element of the type described by E. E. Simmons, Jr. in United States Patent No. 2,292,549, issued August 11, 1942, of which divisional Patent No. 2,365,015 issued December 12, 1944, said element being bonded throughout to the member so that its resistance is varied by deformations in the shape of the tubular portion thereof. An evacuated pressure reference chamber may either surround the member or the member itself may be evacuated to form the pressure reference chamber for the purposes which will be described below. Conduit means are provided to permit the application of the ambient fluid presapplications.

sure in the well to the inside of the tubular member, if the latter is surrounded by the evacuated space, or to the outside wall of the member if the latter is closed and is evacuated internally. Preferably, temperature compensation for the resistance element is provided by a second unstressed unit in the manner common to Wheatstone bridge A suitable multi-conductor electric cable extends from the bonded resistance filament and compensating means just described to the surface of the earth where it is connected to a recorded or Wheatstone bridge indicator, preferably of an electronic type which will indicate accurately the changes in resistance of the bonded filament element due to deformation of the tubular member under pressure change.

It is an object of this invention to provide a pressure gauge which may be made small in diameter and therefore adapted to be run into small diameter tubing, drill pipe and the like.

Another object is to provide a pressure gauge which has no moving parts which would be susceptible to damage by exposure to well fluids which may be at high temperature and of a severely corrosive nature.

Another object is to provide a pressure gauge of this type in which the active element may readily be tested at the surface by means which are portable so that accurate calibration may be had immediately prior to and following a measuring operation in a Well.

Another object is to provide a pressure gauge construction which may be disassembled to permit the use of pressure responsive elements having various effective ranges of calibration, so that maximum sensitivity may be obtained within the range of pressure desired to be measured.

Another object is to provide a procedure for determining whether or not the evacuation of the pressure reference chamber has remained as complete as is required without disturbing the sealing means for said chamber.

These and other objects and advantages will be more fully apparent from the following description and from the accompanying drawings which form a part of this specification and illustrate a preferred embodiment of the invention.

In the drawings,

Figure l is a vertical sectional View of a housing with a pressure responsive element mounted therein and having an evacuated chamber surrounding said element.

Figure 2 is a vertical sectional view of a cable terminal connector for the housing and element of Figural.

Figure 3 is a vertical sectional view of an alternative form of pressure seal for the electrical connections to a pressure responsive element.

Figure i is a transverse sectional view on line IV-IV of Figure 1 showing a form of valved pas sage leading to the evacuated pressure reference chamber surrounding the responsive element.

Figure 5 is a vertical and part sectional view .of

an assembled gauge showing a form of passage 7 leading from the outside of the gauge to the pressure element therein.

Figure 6 is a part sectional plan view of a casing in which the active element of the gauge may be placed for evacuating the pressure reference chamber thereof where the latter surrounds the pressure responsive element.

Figure 7 is a vertical sectional view on line VII-VII of Figure 6 showing an arrangement for sealing the external type of pressure reference chamber while it is under vacuum.

Figure '3 is a vertical sectional view on an alternate form of unit, in which the pressure responsive element is evacuated to form the pressure reference chamber.

Referring to the drawings and particularly to the embodiment of Figures 1 and 5, reference numeral Ill designates generally a hollow cylindrical metal housing which is threaded at its upper end H to engage a similarly threaded hollow cylindrical spacer; i2, threaded at its upper end l3 to enage a correspondingly threaded cable anchorage member i l. Anchorage M is recessed as shown (Figure 2) to receive the several metal-armored strands of an electrically insulated cable It, the latter adapted to extend to the upper end of the well tubing into which the device is to be lowered and having a smooth outer surface to make a pressure tight seal with a stufllng box at the well head.

Inside of the armored strands I5 of cable I6 are suitably insulated copper conductors ll, preferably four in number. These extend downwardly through spacer member !2 to a terminal block at the upper end of housing It. lower end of housing It, which is threaded as at [8, is a correspondingly threaded guide member 19 having at its upper end a plurality of ports 20 which communicate with a recess 2| within the bod of member l9. The weight of that member is so proportionedas by making it of a "heavy metal, or filling part of it with mercury or lead, that it will carry the whole assembly downwardly through the fluid in a well tub- .ing and is desirably of such a value that the pressure within the tubing exerted over the cross-sectional area of cable iii and tending to force the cable out of the usual stuffing box at the top of the well tubing will be overcome, as is Well known in this art. Flattened portions 22 may be provided as desired on part 24 of housing is; cable anchorage member i i, and guide member 19 to facilitate making and breaking the 7 thereto by means of a gasket 25 of bronze, zinc,

Or other soft metal.

The upper end of plug 24 is fitted with a threaded recess 23 to receive the correspondingly threaded lower end of a tubular pressure member 21, the latter provided with a hexagonal or squared portion 28 to facilitate its the latter being At the assembly in the upper end of plug 24. Inter mediate the ends of pressure member 2! at a point where it is of uniform thickness and symmetrical shape there is secured to its outer surface a resistance winding 29, bonded throughout its effective length to member 27 by suitable high temperature resistant and electrically insulating cement. Detailed instructions for the construction of such .a deformation responsive winding are given in Simmons Patent No. 2,292,549 referred to above. Briefly, this involves the use of a fine wire filament, for example approximately 0.001 inch diameter of nickel-copper allo electrically insulated from and mechanically bonded throughout its effective length to tube 21 by means such as a lacquer, for example Glyptal, manufactured by General Electric Company. Suitably insulated leads 30 connect the end of winding 29 to connectors 3! carried by a terminal block 32 at the upper closed end of tube 27. Block .32 be secured at this point by a machine screw 33 and an alignment pin 34.

A second or temperature compensating winding 35 having the same electrical characteristics as the deformation responsive winding 29 is positioned upon a rigid support 36 which is suitably placed adjacent tube 2? so as to reach quickl the same temperature as that tube but is arranged to be independent of any deformation of the tubular pressure member. Suitable leads 3% connect winding 35 with additional connectors 3i on terminal block 32.

The upper end of the hol-ow portion of housing iii may be closed by the means shown in Figure 1 or the alternative means of Figure 3. In Figure 1 the closure and conductor carrying means consist of an elongated metal plug 39 received in a suitable'bore extending throughout the threaded portion i l of housing it. The lower end of plug as is slotted as at ill to straddle a pin All extending transversely across the bore, to prevent undeslred rotation of the plug 39 when assembling or disassembling the apparatus. upper end of plug 39 in the embodiment of Figure 1 is provided with four uniformly spaced threaded recesses 42, each one adapted to receive a small ceramic or other suitable insulator 43, the latter being held in place by a threaded follower 44 and tightly sealed by metallic gaskets 45. Each of the insulators 43 is provided with a sealed insulated conductor 46 extending longitudinally throughout the length of plug 39 and the upper hollow portion of housing it to terminal block 32. The upper ends of conductors 4B are suitably connected to the conductors ll of cable 15, allowing sufficient slack so that the threadedjoint I! may be made or broken without damage to the conductors. A gasket 41, which may be of zinc, bronze, or other soft metal,

is adapted to make tight the threaded joint II s between housing is: and spacer member ii.

The alternative form of closure for the upper of chamber ii? in housing it; is similar in. most respects but instead of having separate ceramic insulators for each of theinsulated conductors Any desired arrangement may be provided for The connecting the bore of the tubular-pressure member 21 with the space surrounding housing In this example an eccentric passage 48 leads from the lower end of threaded recess 25, into which tubular pressure member 2! is adapted to be screwed, to the bottom face so of the plug 24 which closes the lower end of the hollow cylindrical housing iii. As shown in Figure 5, the lower end of passage 43 therefore communicates with recess 2% at the upper end of guide member l9, the latter being provided with a plurality of ports 2!], so that ambient fluid pressure is transmitted through the passage means just described to the bore of tubular member 27:.

One of the principal features of this embodiment of the invention appears to reside in the provision of an evacuated pressure reference chamber surrounding tubular member 271' within the hollow cylindrical housing In this exam ple chamber 3? is evacuated to a pressure of approximately 0.61 of mercury, which has several desirable results. The principal one is to prevent changes in pre sure within chamber 3'! with changes of ambient temperature, these latter often mounting to several hundred degrees in the normal use of this instrument. This provision has eliminated one of the principal causes of error inherent in previous instruments. in addition, the evacuated space forms a known and constant reference pressure with which the pressure within the bore of tubular member 2? compared. To evacuate chamber 3? there provided in plug 24 between the threaded portion 23 and the threaded recess 23 a passage 5i"; which leads to a transverse bore 5!, the latter having a sharp shoulder or valve seat adapted to be closed by a threaded valve plug 52 of brass or soft metal. A second threaded plug 53 is adapted to be screwed into correspondingly threaded portion of transverse bore 5i to secure the valve member in its tightly closed position. An intersecting bore 5 leads outwardly from bore 5! outside of the valve seat through plug 24 to its outer urface, thus completing the passage between chamber '3'! and the outer portion of plug 26 so that evacuation of the gases within the chamber may be completed to the degree desired. Desirably, the outer end of bore 54 is threaded as at 55 to receive a correspondingly threaded plug 55, the latter serving to keep dirt and well fluids from bore 54.

In order to insure that the pressure reference chamber 3? is evacuated to the degree desired, the assembly of Figure 1 may readily be tested by simply immersing it in a heated or cooled fluid. Using a suitable Wheatstone bridge of the conventional type or one of the recently improved electronic varieties connected in the conventional manner to the several conductors ll ex tending from the top of the active element or housing is, no change in the resultant or overall resistance of windings 253 and 35 should be observed by such a procedure. If, after a suitable period has elapsed so that all parts are at the same temperature, there is an indication of change of resistance, this change will indicate to the observer that the evacuation of chamber 3? is not complete and that some expansion or contraction of the remainin ggases has taken place therein, causing a deformation of tube 2T. Obviously suitable correction should be made for whatever hydrostatic head of fluid is imposed upon face 49 and the bore of tubular member 21 by the immersion just mentioned.

Figures 6 and 7 illustrate a preferred arrangesomewhat exaggerated in this View and is desigwhich may be made tight with bolts 52 against a gasket 63. At one side of easing ill is a connection 64 leading to a suitable portable vacuum pump or other source of reduced pressure (not shown). At one side of casing 57 and adapted to be aligned with the transverse bore 5! in plug v24 of housing H3 is a slidable and rotatable shaft 65 received in a transverse housing 53, the latter provided with a packing gland ii? and follower $8. Lubricating means, such as a port closed by a plug 69, may be employed further to seal shaft E5. The inner end of that shaft is squared as at l!) to engage the correspondingly recessed threaded valve 52 so that it may be selectively moved to open or close the evacuation passage formed by bores 55 5| and 5% in plug M. A handle ii on the outer end of shaft '55 facilitates the operation just described.

Figure 8 illustrates an alternative arrangement of this invention in which the generally tubular pressure responsive member is evacuated and then hermetically sealed to form the constant reference pressure chamber, in which case it is usually convenient to bond the resistance winding to the outer wall of the chamber at a point removed from the rounded ends so that it will be truly responsive to mechanical deformation of the chamber under ambient pressure.

Referring to that figure, reference numeral 82 designates the threaded hollow cylindrical spacer described above, at the upper end of which is the cable terminal arrangement shown in detail in Figure 2 from which insulated conductors l? lead downwardly to a terminal block the latt secured by screw 33 to a threaded interi iate support member enerally designated 8i. Guide member 59 is threaded as at it connect to the lower end of member 8% and extend downwardly therefrom. Ports 2 3 permit access of ambient fluid to recess 21, which in this case may be somewhat longer than the embodiment of Figure 5.

Secured to the lower face of member Si and projecting into recess 2i is a closed, generally tubular member Ell which may be made of a strong elastic material such as nickel-iron alloy, ductile tungsten or even a vitreous elastic material such as fused quartz, the wall. thickness, diameter and the like being chosen to give the required deformation-pressure characteristics for the ambient pressure conditions to be determined. If necessary this chamber-forming means may be electroplated, surface work harde' or otherwise treated to prevent migration of light hydro carbon or other gases therethrough under the high pressures and temperatures which may be encountered in certain deep wells. The lower end of tubular member 2H is sealed ofi after evacuation as shown at 82.

In this embodiment, due to the presence of ambient fluid in chamber 2 i, the resistance winding requires somewhat more care in the electrical, moisture, and oil resistance insulation which is hated by reference numeral 29 l. Insulated leads til connect. the ends of. windin 29 to, conn q mi 13-! carried by terminal block 32 as in the embodiment of Figure 1.

The second or temperature compensating wind- -'ing 3:5 is desirably located upon its support 3% sulation for winding 35 as .well as for conductors H, at! and ,38, as will be apparent to one skilled in this art. Although .bothembodiments shown illustrate the resistance winding 28 bonded to the outer wall of the generally tubular pressure iresponsive member '27 and 2? I, .it will be apparent that those windings could equally well be placed, although perhaps less conveniently, on the inside wall of those tubular members to be responsive to mechanical deformation thereof.

In order to obtain the maximum sensitivity from this device, it is desirable-to provide several sizes or wall thicknesses of pressure responsive chamber forming means so proportioned that they will be responsive to various pressure ranges, for example 0 to'2,000, 0 to 4,000, 0 to 6,000 pounds per square inch. With the arrangements shown substitution of one pressure responsivechamber with its associated resistance windings for another of different pressure rating may readily be accomplished.

In conclusion, it will be appreciated that the foregoing specification describes and illustrates one or more examples of an improved well pressure gauge adapted to be lowered upon a multiconductor cable through a well tubing, the cable serving to connect the active resistance elements of the gauge to a suitable Wheatstone bridge or other type of indicator at the surface, characterized essentially by the provision of means forming a generally tubular pressure responsive chamber, one wall of which is exposed to ambient fluid pressure and the other wall of which is exposed to a constant reference pressure substantially below atmospheric, with a suitably insulated resistance winding associated with the member and elastically bonded to one wall thereof so that its resistance changes in response to mechanical deformation of the member due to ambient pressure. There is usually required a second similar resistance winding exposed to the same ambient temperature to compensate for temperatures other than the one at which the device .is-calibrated. he s cond resistance wi dinc being mounted upon a. supp rt wh i dependent, of mechanical deformation of the pressure responsive chamber.

Ihe present application is a divison of my copending application Serial No. 569,691 filed December 26,1944, now Patent No. 2,421,997, issued ,June 10,1947, and is directed to methods of determining the relation between pressure and depth or fluid flow conditions in, oil wells as hereinabove described.

Although only two embodiments or examples have been illustrated and described, it is ob- Vious that numerous changes in the arrangement other than those suggested herein could be made without departing from the invention,

and all such modifications and changes that come within the scope of the appended claim areembraced thereby.

I claim:

A method of testing the degree of evacuation of a temperature compensated resistance element type of pressure gauge having an evacuated pressure reference chamber having a first resistance element responsive to deformation of said chamber, and a second temperature compensating resistance element, comprising the steps of connecting said resistance elements to an in dicator, successively immersing said gauge in fluids at predetermined temperatures difiering from each other and within the range to which the gauge will be used, and determining from the response of said indicator the degree of evacuation of said chamber.

WILLIAM R, POSTLEWAITE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,227,938 Krebs Jan. 7, 1941 2,299,867 Wclison Oct. 27, 1942 2,316,974 Lumm Feb. 16, 3.943 2,318,724 Temple May 11, 1943 2,357,353 Pearce Sept. 5, 1944 2,421,907 Postlewaite June 10, 1947 FOREIGN PATENTS Number Country Date 479,18 i Great Britain Feb. 1, 1938 OTHER REFERENCES Publication, A Bath for use in Graduations 20, April 1943. 

